The invention relates to a clamp for aligning a pair of tubular members (i.e. pipes) in a fixed, end to end relationship, and further relates to a method for using the clamp. According to typical practice, once the tubular members are so aligned, the ends can be welded together.
The type of alignment clamp heretofore used most extensively comprises a pair of clamp sections, where each clamp section includes a pair of longitudinally spaced, semiannular members; a number of cross bars having their outer surfaces welded to the inner surfaces of the semiannular members; and a latch mechanism for latching the clamp sections in clamped engagement with a pair of aligned tubular members. The clamp sections have ends that are pivotally connected, and opposing ends that are drawn together by the latch mechanism to latch the clamp around the aligned tubular members. Various latch mechanisms have been employed, including a hydraulic jack, bolts and nuts, a ratcheted screw, and a mechanism operable by a hand lever.
With regard to the latch mechanism, the hydraulic jack, bolts and nuts, and ratcheted screw are very slow to operate in moving from an unlatched to a latched position. Furthermore, each of the hydraulic jack and ratcheted screw are relatively expensive, and can be easily tightened too far by an operator to result in deformation of the tubular members or damage to the clamp. The hand lever mechanism overcomes these problems in being quick to operate, simple and inexpensive in construction, and in providing a fixed stroke of the hand lever that limits the clamping force exerted by the mechanism. These attributes make the hand lever mechanism particularly suitable for use in aligning tubular members of relatively small diameters of 12 inches or less, where speed of operation is desirable and excessive clamping force is to be avoided.
One problem with the prior hand lever mechanisms, however, is the undesirably large friction-bearing surface areas, or those surface areas in frictional contact during operation. This problem is due to a typical design employing a shaft integrally connected to the hand lever and permanently but rotatably mounted in a sleeve at the latching end of one clamp section. Tie rods have ends pivotally and eccentrically (off-center) connected to respective ends of the shaft, and further have opposing ends secured to a latch bar. The latch bar is adapted to engage recessed surfaces at the latching end of the other clamp section. Rotation of the shaft by manipulation of the hand lever draws the latch bar toward the shaft, thereby urging the latching ends of the clamp sections toward one another. The shaft must necessarily have a diameter larger than the distance of movement of the latch bar relative to the shaft when moving from the unlatched to the latched position, thus contributing to the large friction-bearing surface areas of the shaft outer surface and the sleeve inner surface. This problem is compounded by the dirty and gritty conditions in the field which generally worsen the frictional resistance encountered in operation, thereby requiring more effort on the part of the operator and consequent slower operation of the latch mechanism.
Other problems with the above-described prior alignment clamp include: undesirable accessibility to the "weld areas" between the semiannular members of the clamp sections; contact of only the cross bars with exterior surfaces of the tubular members, thus contributing to the possibility of deformation of the tubular members and instability of the clamp as engaged with the tubular members; inability to clamp tubular members with their ends outside the areas between the semiannular members of the clamp sections, which can be desirable when one of the tubular members is a pipe fitting having a neck length insufficient to extend into such areas or when obstructions prevent positioning of the clamp relative to the tubular members so as to permit positioning of their ends in such areas; and labor intensive and costly weldment construction.